An autostereoscopic display device of the type described in the opening paragraph is known from U.S. Pat. No. 5,969,850.
Basically, a three dimensional impression can be created by using stereo pairs (two different images directed at the two eyes of the viewer), holographic techniques, or multiple planes in the displays. With the multiplanar techniques, a volumetric image is constructed, in which the 2D pixels are replaced by so-called voxels in a 3d volume. A disadvantage of most multiplanar displays is that the voxels produce light, but do not block it. This leads to transparent objects, giving quite literally a ghostly and unpleasant appearance to the displayed images.
Stereoscopic displays do not suffer from this problem. There are several ways to produce stereo images. The images may be time multiplexed on a 2D display, but this requires that the viewers wear glasses with e.g. LCD shutters. When the stereo images are displayed at the same time, the images can be directed to the appropriate eye by using a head mounted display, or by using polarized glasses (the images are then produced with orthogonally polarized light). The glasses worn by the observer effectively route the views to each eye. Shutters or polarizer's in the glasses are synchronized to the frame rate to control the routing. To prevent flicker, the frame rate must be doubled or the resolution halved with respect to the two dimensional equivalent image. A disadvantage with such as system is that the two images produce only a limited “look around” capability. Furthermore, glasses have to be worn to produce any effect. This is unpleasant for those observers who are not familiar with wearing glasses and a potential problem for those already wearing glasses, since the extra pair of glasses do not always fit.
Instead of near the viewers eyes, the two stereo images can also be split at the display screen by means of splitting screen such as a parallax barrier, as e.g. shown in U.S. Pat. No. 5,969,850.
Although these displays are autostereoscopic in the sense that no special glasses are required to view the 3D image, they often work only for one viewer at a fixed position in space. The viewing zone is very narrow. Outside the viewing zone, the observer sees multiple images or a stereo inversion, leading to a very unpleasant view. In practice this means that for many application, for instance in living rooms, the viewing zone is so small that the viewer has to be seated at one particular spot to be able to see a 3D image. Solution which offer multi-view images do so at the cost of resolution.
The device known from United States Patent U.S. Pat. No. 5,969,850 offers a solution to the narrow viewing zone problem by using a dynamic parallax barrier, i.e. a parallax barrier wherein the barrier slits move across the screen.
Although it is possible to obtain a multiview autostereoscopic display in the manner described in U.S. Pat. No. 5,969,850, a drawback of the above described principle is a lack of efficiency. Only a small amount of the light emitted passes the dynamic parallax barrier. For instance, if we use a parallax barrier display with 1000 slots (so, 1000 subframes), we have a horizontal resolution of 1000 pixels. However, the light shines on the whole backside of the parallax barrier and the latter blocks 99:9% of the light. So, for a television application we need at least a very high light intensity to get a sufficiently bright picture. Although the efficiency can be improved by making several slots of the dynamic barrier transparent at the same time, the principle problem of a very poor efficiency remains and in order to be able to use several slots the amount of different viewing directions has to be compromised